A photoreceptor need to have a capability of holding a surface charge in the dark, a capability of generating a charge upon receipt of light and a capability of transporting a charge upon receipt of light. A single-layered photoreceptor having these capabilities in one layer and a functionally—separated multilayered photoreceptor having a layer mainly generating a charge and a layer holding a charge in the dark and transporting a charge upon receipt of light are known.
When an image is formed using a photoreceptor, the photoreceptor is charged in the dark by corona discharge, the charged photoreceptor is irradiated to form an electrostatic latent image, the electrostatic latent image formed on the photoreceptor is developed with a toner to form a toner image, the toner image is transferred and fixed on a recording medium such as papers, and the photoreceptor is discharged and the toner remaining thereon is removed after the toner image in transferred.
Organic photoreceptors have practically been used recently because of their advantages such as flexibility, thermostability and film formability.
Further, electrophotographic image forming apparatuses are rapidly required to produce better quality full-color images and at higher speed. In addition, they are demanded not only in typical office fields, but also in SOHO or light printing fields. Particularly, in the light printing fields, the printing volume noticeably increases and the image quality stability is more required. Therefore, it is indispensable for the organic photoreceptors to have durability.
Some photoreceptors are known to include protection layers on their surfaces. Methods of irradiating light or an electron beam are known to form the protection layers.
Japanese published unexamined application No. 2005-140825 discloses an electrophotographic photoreceptor including an electroconductive substrate, and a charge generation layer, a charge transport layer and a crosslinked charge transport layer sequentially layered on the substrate. The crosslinked charge transport layer is formed by crosslinking a tri- or more functional radical polymerizable monomer without a charge transportable structure and a monofunctional radical polymerizable compound having a charge transportable structure.
However, this is required to improve gas resistance and prevent production of images having uneven image density when used for long periods.
Because of these reasons, a need exist for a photoreceptor having good durability and gas resistance and preventing production of images having uneven image density even when used for long periods.